Production of dienes



Patented Jan. 18, 1944 PRODUCTION OF DIENES Martin de Slmo, Piedmont, and Robert M. Roberts, Berkeley, Calif., assignors to Shell Development Company, San Francisco, Cali! a corporation of Delaware Application May 27, 1941, Serial No. 395,356

10 Claims. (Cl. 260-680) corresponding alcohols, etc. These methods,

however, have certain disadvantages, for example, the cost involved in preparing the starting materials.

It is also known that cracking of hydrocarbonsoften yields minor proportions of dienes, particularly of butadiene. The proportion of the diene in the cracked products is, however, small and it is associated with major amounts of saturated and ethylenic hydrocarbons having nearlyg equal vapor pressures. Thus. the recovery of the dienes is diflicult and their yields are small.

It is an object of this invention to provide a process for the manufacture of valuable hydrocarbons, especially dienes and particularly pentadienes, by cracking a selected hydrocarbon stock which is readily available. Another object is to produce hydrocarbon fractions rich in diand mcno-olefines and aromatic hydrocarbons, respectively, from which the dienes can be separated in a simple manner. Still further objects include simplified procedures, decreased cost in the manufacture of dienes, and other improve ments found hereinafter.

We have found that gases obtained by vapor phase cracking of oleflne polymers contain substantial amounts of dienes and that selected fractions of such gases may comprise major proportions, i. e. over 50%, of pentadiene and particularly of isoprene.

According to this invention, a cracking stock composed of normally liquid olefine polymers obtained by polymerizing normally gaseous olefines, and preferably of dimers, trimers or tetramers of propylene or their mixtures, is cracked in the vapor phase at temperatures above about tylenes.

600 C. and pressures not substantiallyabove atmospheric for a time to gas ify and transform in one or several passes a major portion of said polymers into normally gaseous products.

The normally liquid oleiine polymers which comprise the cracking stock of this process may be obtained from ethylene propylene, butylenes or amylenes, or a mixture thereof by thermal or preferably catalytic polymerization. These polymers comprise predominantly branched acyclic'mono-olefln'es including substantial amounts of tertiary olefines. A cracking stock which boils within the gasoline range and especially one boiling below about 150 C. is preferred, giving in general higher yields of dienes. However. it may include or may consist essentially of products boiling above about 150 C.

When compared with the known process of producing dienes by thermal treatment of butylenes, our method has the advantage of using as a cracking stock a feed which predominates in readily-available mono-oleflnes, all of which yield high percentages of dienes on cracking. In order to produce a comparable butylene feed from gases containing butylenes, it would be necessary to resort to complicated and expensive fractionations. Thus, the use of the polymers simplifies the production of dienes in relatively high concentrations and makes it more economical than the correspon ng cracking of bu- Moreover, polymers of ethylene and propylene formsuitable cracking stocks, whereas the monomers upon cracking do notyield substantial amounts of dienes.

The vapor phasecracking is conducted so as to gasify 15%85% of the feed per pass. We define as gasified that art of the cracking products which consists of molecules having less than six carbon atoms.

The cracking temperature, 1. e. the, maximum temperature to which the cracking stock is heated, is above 600 0., preferably 650 C.-850 C.

The resulting cracked products are quenched from them dienes which constitute substantial proportions thereof are isolated by conventional methods. Other products obtained in this process include. besides the dienes, tar and products heavier than gasoline, gasoline and,gases lighter than gasoline containing high percentages of mono-olefines. q

These products may be withdrawn, treated and used as may be convenient. Certain portions of them may, however, advantageously be utilized within the process. Thus, mono-olefines may be repolymerized to polymers which then may formpart of the stock for the cracki process. e

The composition of the cracked gasoline fraction varies with the intensity of the cracking. i. e. it may be predominantly oleflnic,- e. g. having substantially retained the' composition of the cracking feed if the original cracking stock boils within gasoline boiling range, or it may have become more or less aromatic.

If the cracking is relatively superficial, i. e.. the gasiflcahon per pass is of the order of 25%, for example %-40% and preferably %-30%, the ungasified portion of the cracking stock is predominantly olefinic. The latter is advantageously recracked and treated like the original cracking stock, for example, by recirculation as part of said stock.

-If the cracking is deep, i. e. the gasiflcation is of the order of 65%, for example 50 75-85% and preferably 60 96-70%, the gasoline fraction of the cracked products may contain substantial amounts of aromatic hydrocarbons which apparformation such as copper-containing alloys, e. g.

aluminumor phosphor-bronze, or refractory ceramics, are thus preferred in the construction of surfaces which are exposed 'to hydrocarbons ently are formed by secondary reactions such as polymerization or condensation of the primary products. In this case, it is advantageous to separate valuable aromatic hydrocarbons such as at cracking temperatures.

The velocity at which the gases passthrough the cracking zone depends on the exact result desired, the temperature and pressure of cracking, and the dimensions of the cracking zone. The space velocity necessary to produce the desired degree of gasification increases rapidly as the cracking temperature is raised. The real velocity of the gaseous hydrocarbons in the cracking zone is very diflicult to determine accurately because the volume of the cracking stock changes rapidly under the cracking conditions. Therefore, in defining this invention, we prefer to utilize the concept of liquid space velocity which is the liquid volume of the feed delivered to the cracking zone per volume of said zone per hour. The cracking zone is defined as the space occupied by gas in which the temperature is within 20 C. of the maximum cracking temperature. Liquid space vel city can be accurately measured and, for a given pressure, temperature and dilution, determines the real space.velocity of the vapors.

pur process is illustrated in the accompanying drawings which represent simplified flow diaselves, or may interfere in the cracking because of their tendency to polymerize, or in the recovery of aromatics with the aid of selective solvents grams of two embodiments of this invention.

Figure I illustrates theprincipal steps of this process.

Figure II illustrates a useful modification of this process.

For simplicity, the drawings do not show pumps, heat exchangers, valves, by-passes, vents, reboilersl, condensers and other auxiliaries, the proper p acement of which will be at once evident to Itllliose skilled in the art.

the embodiment illustrated in Figure I gases containing oleflnes enter the polymerization zone 3 through conduit I.

because of their solubility therein, which comes from an outsidesoul'ce not Shown u h ine 9 ents may be found in this fraction. These may? advantageously be separated from tars and, if necessary, from aromatics and poly-olefines and be returned for further cracking.

The cracking in this process is conducted at pressures of about atmospheric or below, and preferably not substantially above 100-150 lbs.

p. s. 1. Thus, pressures above atmospheric sufli- I cient toovercome the resistance of conduits, con-- densers and other equipment which follow the cracking zone may be maintained therein. If desired, the cracking may be, conducted in the presence of steam, nitrogen and other substantially inert gases. Amounts of these gases up to 80% by weight of the mixture may be used;

The heating of the hydrocarbons to thiscrackand are advantageousl supplemented by gases produced within this process, as will be described later, and supplied through conduits 5 or 'I, or

both. It is desirable that these gases contain a substantial proportion of propylene and may be mixed and compressed by conventional means not shown.

The olefines contained in the gases supplied to The resultin polymers are-conducted through line H to the polymer stabilizer l3 wherein the polymers are separated from the unreacted gases which are taken overhead through lin l5 and mg I raturemay be achieved! Contact with may either be withdrawn completely from the These gases are admitted aseasoo process through line l'l, or be returned in part to the polymerization zone 9 through conduit 1.

The stabilized polymer is taken through line l9 and is advantageously commingled with recycle liquids, produced in the system as hereinafter idescribed and introduced through line 94. The mixed liquids are led into cracking coil 20 in fur nace 2| in which the desired conditions of temperature, pressure and residence time are maintained, for example, at 750 C., atmospheric pressure and a liquid space velocity of 200, so as to efiecta gasiflcation of about 25 The cracked products leave reaction coil 20 through line 23 and are separated from tars and other relatively heavy' materials in fractionator 25. The lighter products including gases, naphthaand, if desired, gas oils are takenoverhead through vapor line 29. The heavier products are withdrawn from the system through line 21.

The products in line 29 pass into stabilizer 3| wherein an overhead fraction consisting essentially of C5 and lighter components is separated from a heavier naphtha fraction; this latter, substantialiy free of C5 and lighter components, is taken through line 33 and may go through line 35 to storage not shown, or preferably may be retiigxnied through lines 34 and 19 to the cracking coi If desired, the dioleflnes contained in this naphtha fraction may be separated in zone 32, for example, by extraction with a suitable complex-forming reagent, e. g. CliClz, AgCl, S02, etc., or by polymerization with or without suitable catalysts such as poly oxy acids, e. g. H2504, HaP04, etc., or Friedel-Crafts catalysts, or by the Diels-Alder reaction involving maleic acid anhydride-type reagents, etc.

The overhead C5 and lighter fraction from stabilizer 3| is taken through conduit 91 to a i'ractionating system wherein it is subjected repeatedly to fractional distillation. In column 39 a bottom fraction is produced comprising predominantly hydrocarbons having five carbon atoms which is taken through line ll, and a lighter fraction substantially free from C5 components. The latter is taken overhead through line 43 to fractionator 45, where a bottom fraction comprising predominantly hydrocarbons having mostly four carbon atoms is produced and withdrawn through line 41. Remaining ases substantially free from 04' and heavier components are taken overhead through line 49 into fractionator 5| where hydrocarbons having two and three carbon atoms are separated as the bottom fraction and pass into line 53. ,Th overhead fraction comprises mainly hydrogen and methane and is withdrawn through line 55 to be discarded from the process.

Thus, separate C5, C4 and C2-C3 fractions are taken through lines ll, 41 and 53, respectively.

The C2-C3 fraction is rich in propylene and ethylene and may, if desired, be eliminated from the process through line 51, but it is preferred to return it through line 5 to the above-mentioned polymerizing zone 9.

The C4 fraction which contains butadiene is led through line 41 to column 59 wherein itis subjected to extractive distillation with a suitable solvent having a relatively high boiling range tacted with the ascending C4 vapors so as to produce a fat solvent charged with substantially pure butadiene which is eliminated from the bottom of the column 59 through line 99? This "fat liquid is separated by fractional distillation in fractionator H into the "lean solvent and butadiene. The butadiene so produced is withdrawn through overhead line 13 while the "lean solvent is drawn off at the bottom throughline SI and is returned to extractor 59. The butylenes and butanes separated from the butadiene in column 59 are taken through line 65 and may be eliminated from the system through line 81. or more advantageously, may be returned to the polymerizing zone 3 through lines 69 and 5.- v

The C5 fraction, rich in pentadiene,- is given a treatment similar to that of the C4 fraction. Line ll lead it to column 15 wherein it is extracted in the vapor phase by a lean solvent supplied through line 11. The fat solvent is drawn oil through line 19, and the residual pentanes and amylenes are taken through line BI and may be eliminated from the proces through line 83, or, if desired, may be returned to the-polymerization zone 3 by way of lines and 5. The fat solvent is fractionally distilled in fractionator 81 to isolate pentadienes which are withdrawn through line 89, while the lean solvent is recirculated through line ll. Suitable solvents for the vapor phase extraction of dienes include, for example, alcohols such as butyl alohols, '{g zmyl alcohpls; icyg ohexanol, tc.; aldehydes such as furfural, aciolin, crotonaldehyde, etc.; ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, acetophenone, cyclohexanone; ethers such as di-isopropyl ether, dichlonechyl ther, diqxane; organic nitrogen bases such as aniline, toluidine, phenylhydrazine, ethylene dlamine, ethanol diamine: phenols such as phenol, cresol, xylenols; esters such as ethylene chlorhydrin, dimethyl phthalate, diethyl tartrate, ethylene dichloride, lactic acid nitrile, acetonitrile, di-isopropyl or allyl sulfate, ethyl borate or ethyl orthosilicate; other organic derivatives of mineral acids such as nitrobenzene, nitromethane, nitroethane, and many other polar compounds. The recovered pentadienes usually comprise ,a mixture of isoprene (l-methyl butadiene) piperylene (n-pentadiene) and cyclopentadiene. This mixture may be either withdrawn through line 9| or, if desired, may b further fractionated to separate the several C5 dienes from one another by leading it through line 92 to vessel 93 where the cyclopenta'diene is dimerized by subjecting the'mixture to moderate heat in the liquid phase. The resulting product is fractionally distilled, the dimer forming the distillation residue which emerges through line 95 to be withdrawn through line 91, or to be regenerated by exposure to high temperature and vacuum ina depolymerizing be carried out in a different manner, if desired.

The cracking in coil 29 may be intensified, for example, by reducing the space velocity to about 20 under the same conditions of pressure and temperature, so as to 'obtain a gasiflcation of about 65%. The naphtha fraction produced under these circumstances and taken through line 93 from fractionator 3| contain aromatic hydrocarbons.

. duced through line I.

These valuable hydrocarbons may be separated and the recycle stock recovered by convenient methods, such as fractional and extractive distillation, or liquid-liquid extraction, or both. For example, the liquid withdrawn through line 33 is led through line I I3 to fractionator I I5 wherein it is split into a narrow Cc overhead fraction taken through line Ill and a bottom fraction of C7 and heavier components withdrawn through line II9. This lin leads to fractionator I2I, wherein another narrow C1 overhead fraction is separated and taken through line I23, and a bottom fraction substantially free from C1 hydrocarbons which is withdrawn through line I25, either to be discarded or further treated as will be described.

The Ca and C1 fractions thus separated are rich in benzene and toluene, respectively. The C5 fraction is conducted through line II1 to column I21,wherein it is subjected to extractive distillation with a lean selective solvent for aromatics introduced through pipe I29. The fat solvent rich in benzene-leaves through line I3I and the residual Cc hydrocarbons are withdrawn overhead through line I33 or returned to the cracking coil 20 through lines 34 and I9. The fat solvent is fractionally distilled in fractionator I35 so that the lean solvent is recovered as the bottom fraction and returned through line I29 to extractor I21, and the benzene is obtained overhead through line I31,

The gaseous C-z fraction is conducted through line I23 to column I39 wherein it is extracted with a lean solution solvent for aromatics intro- The fat solvent rich in The heavier-than-Cv bottom fraction from fractionator I2I obtained through line I25 contains aromatics. arated by liquid-liquid extraction with a liquid having greater solvent power for aromatics than for olefinic hydrocarbons, for example liquid 80:. For this purpose, the hydrocarbon liquid is delivered by line I25 to extractor I26 wherein it is extracted with liquid SO: entering through conduit I23. The raflinate passes through line I39 to a stripper I32 wherein it is stripped of the dissolved SO: and is therefrom preferably returned to the cracking coil 20 through lines I34 and I9. The extract containing aromatics is conveyed from extractor I28 through line I35 into separator I33 wherein a bottom fraction comprising mainly SOs-free aromatics and an overhead fraction of S0: is produced. The aromatics are obtained through conduit I49 while the S02 is taken overhead through line I42 to be liquefied in cooler I44 together with the S0: taken from stripper I32 through line I46. The liquefied S0: is then reintroduced through conduit I29 into extractor I26.

Other solvents suitable forthe liquid-liquid extraction are, for example, nitrobenzene, methyl acetate, phenyl acetate, methyl or ethyl cellosolve, furfural, acetone, aniline, phenol, cresylic acids, dichlorethyl ether, antimony trichloride, SOz-benzene mixtures, or combinations of solvents and anti-solvents suchv as phenol or cresol toluene leaves through line I43, and the residual returned through line I4I to extractor I21. The

toluene is obtained overhead throu h line I49.

Suitable solvents for the recovery of aromatics by extractive distillation are, for example, phenol,

cresylic acids, alkyl phenol mixtures, aniline, al-' kyl anilines, diphenyl amine, ditolyl amines, carbitols (diethylene glycol mono-ethers) such as' methyl, ethyl and propyl carbitols,.chlorinated dialkyl ethers such as beta-beta-dichlorethyl ether, nitrobenzene, nitrctoluene, nitroxylenes, naphthols. alkyl naphthols, benzo phenone, phenyl tolyl ketone, diphenyl ketone, alkyl phthalates such as dimethyl phthalate, alkyl salicylates such as methyl salicylate, benzyl alcohol, benz chlorides, i. e. benzyi, benzal, and benzo chlorides, benzonitrile, diphenyl oxide, ditolyl oxide, hydroxy pyridine, nitropyridine, chlorinated pyridines, quinoline, isoquinoline, chlorinated quincline, hydroxy quinolines, 5-nitro quinoline, tetrahydrofurfuryl alcohol, furfural alcohol, furfural, the mono glycerol ethers, such as l-methoxy glycerol, 2-methoxy glycerol, l-ethoxy glycerol, Z-ethoxy glycerol, l-propoxy glycerol, 2-propoxy glycerol, l-isopropoxy glycerol, 2 -isopropoxy glycerol; the glycerol di-ethers such as 1,2-dimethoxy glycerol, 1,3-di-methoxy. glycerol. 1,2-di-ethoxy glycerol, 1,3-di-ethoxy glycerol, 1,2- di-propoxy glycerol, 1.3-di-propoxy glycerol,1,2- di-isopropoxy glycerol, and 1,3-di-lsopropoxy glycerol; the mixed di-glycerolether esters such as l-ethoxy, 2-methoxy glycerol, l-methoxy, 3- propoxy glycerol, and l-ethoxy, 2-isopropoxy glycerol.

with propane, etc.

be by-passed and all the aromatics separated by liquid-liquid extraction, as described, or alternatively, if desired, the liquid-liquid extraction step may be replaced by further fractional and extractive distillation of the several fractions.

The above embodiment of our invention which utilizes single polymerization and cracking zones is advantageous, if the majority of the oleflnes of the feed to the polymerization zone 3 consists of a single specie,'e. g. propylene. If several olefines are present and in substantial amounts, it may be diflicult to polymerize them completely and simultaneously under one set of conditions without reducing appreciably the life of the catalyst. Furthermore, the polymers obtained are heterogeneous so that the cracking conditions suitable for one may produce excessive or insufllcient gasification of the others.

Thus, when it is desired to utilize several difierent oleflnes in the-feed, the embodiment of this process illustrated in Figure II may be pre- 7 ferred.

Several narrow hydrocarbon fractions, each comprising predominantly a single olefinic specie, enter the process separately. For example, C2,

' Ca, C4 and C5 hydrocarbon gases containing the corresponding oleflnes are admitted from sources not shown through lines I59, I5I, I53 and I55, respectively. Corresponding oleilne-rich gases produced in the system, as hereinafter described,

'may advantageously be added thereto through The latter are preferably sepassasoo Fraction Temperature Pressure The stabilized polymers thus produced are taken through lines I14, I15, I11 and I19 and may be either commingled in lines 'I8I, I82 and I83 to bejcracked in one of the cracking zones I84, I85, I81 and I89, or preferably are led to these zones separately to be cracked so as to obtain the desired degree of gasiflcation of each feed. For example, if the temperature of the cracking zones is 750 C., suitable liquid space velocities are 7, 10, 15 and 20, respectively, so as to gasify about 65% of the feed.

duce an aromatic fraction which is withdrawn through line 221. and an aromatic-free fraction which is preferably Iurther cracked. For this purpose, it may be' returned through lines 229 5 and 2: to one or more of the crackingzones I84,

The cracked products emerging from the furnaces by lines I90, I9I, I93 and I95, respectively,

are commingled with each other and may advantageously be combined with the other cracked 2 products produced in the system, as hereinafter described, introduced through line 231. The resulting mixture is subjected to distillation in fractionation zone I99 so as to produce several narrow fractions comprising predominantly C1 and lighter, C2, C3, C4, C5, C6 and heavier, tively.

The C1 and lighter fraction is withdrawn through line 20 I.

The C2 fraction, rich in ethylene, is obtained through line I56 and preferably returned to the polymerization zone I62.

The C: fraction, rich .in propylene. passes through line I51 and is preferably returned to the polymerization zone I63.

The C4 fraction contains butadiene and is taken through line 203 to be further treated in zone 205 so as to isolate the butadiene which is withdrawn through line 201. The residual gases from this operation, comprising mainly butanes and butylenes, are removed through line I59 and preferably returned to polymerization zone .I 65.

and tar, respec- I85, I81 and I89.k .'1he composition of this fraction is,- however difierent from any one of the original crackingstocks and therefore it is often preferable to crack it in a separate cracking zone 235, to whiclr line 233 leads and where cracking conditions are 'maintained for the desired gasiflcation, for example, at 750 F. at a space velocity of about 25. The cracked products are obtained therefrom through line 231 and are introduced into the fractionating'zone I99 through line I91.

In the embodiment illustrated in Figure II, the cracking has been conducted so as to produce ,both diolefines and aromatics. If it is desired to avoid the production of aromatics, it may be modified by cracking so as to produce a gasiflcation of only about 25%, for example, by lowering the temperature of cracking zones by 50 C. while maintaining the same liquid space velocities or by increasing the space velocity while maintaining the same temperatures. In this case the separation zone 225 is by-passed through line 239.

It may sometimes be preferred to separate the dienes or the aromatics, or both without prefractionation or following a degree of fractionation less thorough than described. Alternatively, it may also sometimes be desirable to produce a sharper fractionation before further recovery or to use directly fractions rich in dienes or aromatics, or both, produced by very sharp fractionation.

The following examples illustrate this process:

' Example I Propylene was polymerized over a phosphoric acid catalyst. The polymer obtained boiled from 72 C. to 218 C., had a density D 20/4=0.7373 and abromine number=134. It was cracked at 750 C. and at a liquid space velocity of 35.5 in a I (calculated in weight percent on the charge) The Cs fraction, rich in pentadienes, is conducted through line 209 to zone 2 wherein pen- I tadienes are recovered and withdrawn through line 2I3. They may, if desired, be further separated in separating zone 2I5 so as to yield-substantially pure isoprene, piperylene and cyclopentadiene which may be taken through lines 2", II9 and 22I, respectively. The residual Cs gases containing substantial amounts of amylenes are eliminated from the diene-recovery zone 2 through line I6I and are preferably returned to polymerization zone I61. g

The separation of dienes may be conducted as described above by extractive distillation or other vapor phase extraction with similar solvents; or by azeotropical distillation in the presence of anhydrous ammonia, methylamine, C02, lower aleohols, etc.; or by liquid-liquid extraction with acetone, furfuraLaniline, phenol, etc.; or through formation of complex compounds with copper or silver salts, S02, etc.; or by polymerization under the influence of heat, pressure, light, or catalysts such as Na, K, H2804, HaPOr, PzOs, AlCla, etc.;

Per cent Hydrogen .4 Methane and lighter 11.6

C: cut (63% ethylene) 13.6

C: out (90% propylene) 9.6

Butadiene '2.3

Other C4 (93% butylenes) 7.6

Pentadienes 7.7

Other Cs (93% amylenes) 5.8

Heavier-than-Cs and loss 41.1

Example II I Butylene was polymerized over phosphoric aci catalyst. The polymer obtained had a density D 20/4=0.7403, a bromine number=150, an initial boiling point of 75" C. and a 95% point of 300 C. It was cracked at 700 C. and at a liquid space velocity of 13.2, giving a gasiflcation of 55%. The products comprised:

Per cent Hydrogen .2 Methane and lighter 10.6 C: out (68% ethylene) 8.8 C: out (73% propylene) -1. 10.8" Butadiene Y 1.3 Other C4 (83% butylenes) 9.1 Pentadienes 5.7 Other Ca (92% amylenes) 6.3

s led into zone 225 wherein it is to pro- Heavier-than-Cs and loss.'-- 45.2

' Example 111 The propylene polymer described in the first example was cracked at 740 C. so as to give a ga'sification of 61%. The products were:

Percent of I fraction- Percent of feed Hydrogen Methane H. C: out (75% ethylene) C: out (92% propylene).

wove-swl'oly-olefines. Other hydrocarbons... 00 C.l25 0. fraction.

Toluene The pentadienes had the following composition:

. Per cent Isoprene 79 Plperylene I 9.5 Cyclopentadiene 11.5

The original polymer had an A. S. T. M. octane number of 83. The gasoline boiling from 55 C. to 200 C. obtained from the cracked products in a. yield of 26.8% had an octane number of 86.

We claim as our invention:

1. In the process of manufacturing dienes, the steps comprising thermallycracking in the vapor phase at temperatures between 650 C. and 850 C. normally liquid polymers of propylene so as to gas lfy 15%-85% thereof, and separating dienes from the resulting cracked products.

2. In the process of manufacturing dienes, the steps comprising treating gases containing monooleiines having 2 to 5 carbon atoms inclusive in a polymerization zone in the presence 'of a solid phosphoric acid catalyst to produce normally liquid olefine polymers, separating all of said liquid polymers, thermally cracking them in the vapor phase between 650 C. and 850 C. so as to gasify 15%-85% thereof, whereby dienes and olefines are formed, separating from the resulting cracked products dienes and fractions containing oleflnes ing the latter to said polymerization zone.

3. In a. process for manufacturing dienes, the

steps comprising polymerizing gases containing mono-olefines having 2 to 5 carbon atoms inclusive in a polymerization zone in the presence of a solid phosphoric acid catalyst to produce normally liquid olefine polymers and residual gases, saparating said polymers from said residual gases,

thermally cracking in the vapor phase at a temperature between 650 C. and 850 C. all of said liquid polymers and a recycle oil produced in the process so as to gasify 15%-85% thereof, wheremally gaseous, aromatic and tarry hydrocarbons, g

and a tar fraction: and returning said fraction containing oleflnes to said polymerization zone.

4. A process according to claim 3 wherein the recycle oil is free from polyolefines.

5. In a process for producing dienes and aromatics, the steps comprising polymerizing gases containing mono-olefines having 2 to 5 carbon atoms inclusiv in a polymerization zone in the presence of a solid phosphoric acid catalyst to produce normally liquid olefine polymers and residual gases, separating said polymers from said residual gases, thermally cracking in the vapor phase at a temperature between about 650 and 850 C. all of said liquid polymers and a recycle oil produced in the process so as to gasify 85% thereof, whereby dienes, olefines and aro- 'matics are formed, separating from the combined cracked products at least the following fractions: a diene fraction, an aromatic fraction, fractions containing oleflnes having 2 to 5 carbon atoms inclusive, and said recycle oil which is free from normally gaseous, aromatic and tarry components, and a tar fraction; and returning said olefine fractions to said polymerization zone.

6. In a process for producing dienes, the steps comprising polymerizing in the presence of a solid phosphoric acid catalyst gases containing mono-olefines having 2 to 5 carbon atoms inclusive so as to produce normally liquid polymers and a gaseous residue, separating said polymers from said residue, thermally cracking in the vapor Phase between about 650 and 850 C. all of said liquid polymers and a recycle oil so as to 88.81- fy 15 %-85% thereof, whereby dienes, oleflnes, and aromatics are formed, fractionally distilling the combined resulting. cracked products to produce at least the following fractions: a. light normally gaseous fraction substantially free from oleilnes, a medium normally gaseous fraction substantially free from dienes and containing olefines, a heavy normally gaseous fraction containing oleiines and dienes, a normally liquid fraction containing aromatics, and a heavy residue; withdrawing said light gaseous fraction and said heavy residue, separating dienes from the heavier gaseous fraction, and returning the remainder of said fraction and said medium gaseous fraction to said polymerization zone, separating from said normally liquid fractions polyoleflnes and aromatics, the remainder being said recycle oil which is cracked in the vapor phase.-

7. In a process for manufacturing dienes, the steps comprising separate y po ymerizing in the presence of a solid phosphoric acid catalyst at least two normally gaseous hydrocarbon mixtures containing moho-olefins of different molecular weights in separate polymerization zones to produce normally liquid polymers and residual gases, substantially all the oleflns in any one mixture --havlng the same number of carbon atoms per molecule, separating said polymers from said residual gas, thermally cracking in the vapor phase at a temeprature between 650" C. and 850 C. all of said liquid polymers and a recycle oil produced in the process ,so as to gasii'y 15% to cycle "oil which is free from normally gaseous,

aromatic'and tarry hydrocarbons, and a tar fraction; and returning said gaseous recycle to one of said polymerizing zones as part of one of said normal y gaseous hydrocarbon mixtures.

a,sse,soo

8. In a process of'manufacturing dienes the steps comprising separately polymerizing in the presence of a solid phosphoric acid ca alyst at least two normally gaseoushydrocarbon mixtures containing mono -oleflns oi 'diilerent molecular wei hts in separate polymerization zona to produce from each gaseous mixture normally liquid 7 polymers and residual gases, substantially all the oleilns in any one mixture having the same number of carbonatoms per molecule, separating said polymers from said residual gases, thermally cracking in the lvapor phase between about 650 and 850 C. in separate cracking zones all of eaclfiif said several liquid polymers and a recycle oil produced in the system, whereby dienes and olenns are produced, combining the resulting products dienes and fractions containing oleflns cracked products. separating from said combined products at least the following fractions: a diene fraction, gaseous recycle fractions containing oleflns wherein all the olefin: in any one gaseous recycle fractidn have the same number ofcarbon atoms per molecule, and said recycle oil which is substantially free from normally gaseous, arcmatic and tarry components; and returning the corresponding gaseous. recycle fractions to their corresponding? polymerizing zones as part of said corresponding normally gaseous hydrocarbon mixtures;

having 2 to 5 carbon atoms inclusive, and returning the latter to said polymerization zone.

10. In the process of manufacturing dienes the steps' comprising treating propylene in a polye merization zone in the presence of a solid phosphoric acid catalyst to produce normally liquid oleflns polymers, separatnig said polymers, thermally cracking them in the vapor phase between about 650 C. and 850 C. so as to gasify- 15% to thereof whereby dienes and oleflns are formed, and separating dienes from the resulting cracked products.

MARTIN DI- smo. ROBERT ML, ROBERTS. 

